|dc.description.abstract||Auxin controls plant growth and development through both genomic and non- genomic processes. Genomic processes are regulated through the degradation of a group of transcriptional repressors called Aux/IAAs. Recent studies indicate that IBR5 (Indole- 3-butyric acid response5), a dual specificity phosphatase, also regulates degradation of Aux/IAAs through an unknown mechanism. To better understand how IBR5 regulates plant auxin response, we recently carried out a yeast two hybrid screen to identify IBR5 interacting proteins. ARA2 was isolated as one of the putative IBR5 interacting proteins. ARA2, which is a small GTP binding protein, belongs to Ras super family of proteins.
These GTP binding proteins have pivotal roles in intracellular transport in mammalian, yeast cells, and also in plant in response to diverse environmental stimuli. Several other small GTPases such as ROP2 and ROP6 are also found to be involved in auxin responses in plants suggesting that small GTPases are integral components of auxin signaling. Thus, it was hypothesized that ARA2 play a role in plant auxin responses through interaction with IBR5. Results presented here show that ARA2 physically interacts with IBR5
both in-vitro and in vivo. This interaction occurs through the catalytic domain of IBR5. Also, ARA2 and IBR5 are localized to the same sub-cellular compartments. Further, results show that AXR3NT-GUS degradation and DR5::VENUS expression in ara2-3 background is affected suggesting that ARA2 may be involved in the regulation of AUX/IAA degradation and auxin-induced gene expression. Nevertheless, ara2-3 mutant does not show any altered auxin related physiological responses probably due to genetic redundancy. However, characterization of ara2-3.ibr5-1 double mutant reveals that ara2-3 mutant is a mild enhancer of ibr5-1 mutant phenotype suggesting that ARA2 and IBR5 may function together in modulating the auxin responses in same signaling pathway.||